UNIVERSITY  OF  CALIFORNIA  Agricultural  Experiment  Station 

„..„_      __     A«BI/,lllTllnP  BENJ.    IDE    WHEELER.    PRESIDENT 

cOLLE«t     OF     AGRICULTURE:  THOMAS    FORSYTH    HUNT,  Dean  and  Dircctor 

___„_.    _v  H.     E.    VAN     NORMAN,    VICE-  DlR  ECTOR  AND   DEAN 
DCnKLLLT  University    Farm    School 


CIRCULAR  No.  120 

(September,  1914) 

POTATO  ^GROWING  IN  THE  SAN   JOAQUIN 
AND  SACRAMENTO  DELTAS  OF  CALIFORNIA 

BY 

W.  V.  SHEAR 

Assistant  Horticulturist,  Bureau  of  Plant  Industry,  U.  S.  Dept.  of  Agriculture 


INTRODUCTION 

The  delta  lands  of  the  San  Joaquin  and  Sacramento  rivers  occupy 
an  area  of  about  250,000  acres  of  very  fertile  peat  soil.  They  lie  at 
about  sea  level  and  for  the  most  part  consist  of  a  peat  formation 
made  up  of  more  or  less  incompletely,  decomposed  roots  and  stems  of 
tule  and  other  marsh  plants,  to  which  has  been  added  the  sediment 
deposited  by  the  rivers.  The  depth  of  the  peat  and  the  amount  of 
sediment  varies  considerably  in  different  localities.  Before  these  lands 
were  reclaimed  they  were  flooded  during  the  major  portion  of  the 
year.  The  marshes  are  reclaimed  by  throwing  up  levees  along  the 
rivers  or  sloughs  to  exclude  tidal  and  flood  waters,  while  by  means 
of  ditches  and  pumps  the  water  is  kept  at  a  sufficiently  low  level  to 
permit  the  growing  of  many  farm  crops.  The  additional  water  needed 
for  irrigation  during  the  summer  months  is  brought  over  the  levees 
by  means  of  siphons,  or  through  the  levees  by  the  use  of  headgates. 
The  rainfall  of  this  section  of  the  state  averages  about  15  inches  per 
year,  the  rainy  season  beginning  in  October  and  ending  in  April. 

The  principal  crops  grown  in  the  region  are  potatoes,  barley,  beans, 
and  onions.  A  considerable  acreage  has  been  planted  to  asparagus, 
but  the  area  devoted  to  this  crop  is  becoming  more  restricted  than 
heretofore.  Celery  is  also  grown  to  some  extent.  The  principal  cash 
crop,  however,  is  potatoes  and  an  area  of  from  forty  to  fifty  thousand 
acres  is  annually  devoted  to  this  crop. 

GENERAL  PRACTICES  IN  HANDLING  THE  POTATO  CROP 

During  the  first  three  years  following  the  reclamation  of  these 
lands  they  are  cropped  every  year  to  potatoes.    Afterwards  the  prin- 


cipal  rotation,  especially  in  the  San  Joaquin  portion  of  the  delta, 
consists  of  barley  alternated  with  potatoes  until,  owing  to  the  great 
reduction  in  the  yields,  it  becomes  no  longer  profitable  to  grow 
potatoes.  During  the  first  year  or  two  the  yields  often  run  from 
200  to  300  sacks  per  acre  (350-550  bushels).  At  the  end  of  eleven 
years  (and  this  system  of  rotation  is  sometimes  persisted  in  for  that 
length  of  time)  the  land  has  been  seven  times  planted  to  potatoes  and 
the  yields  run  as  low  as  35  sacks  per  acre.  The  farmers  are  usually 
annual  tenants,  the  potato  growers  moving  each  year  from  farm  to 
farm  and  growing  no  crop  save  potatoes.  The  potato  farm  usually 
comprises  an  area  of  from  150  to  300  acres,  while  the  barley  farm  is 
a  combination  of  several  of  the  farms  planted  to  potatoes  the  pre- 
ceding year. 

Potato  planting  covers  the  period  from  March  to  June,  and  some- 
times extends  into  July.  The  Burbank  potato,  a  rather  late  variety, 
is  grown  almost  universally,  although  often  a  small  quantity  of  an 
early  variety  is  planted  first  in  order  that  the  harvesting  of  the  early 
crop  may  begin  almost  as  soon  as  the  late  planting  is  completed.  The 
land  is  usually  plowed  early  in  the  year  and  again  at  planting  time, 
the  seed  pieces  being  dropped  by  hand  in  the  furrows  behind  the 
plow  at  every  other  round,  this  bringing  the  rows  about  30  inches 
apart.  To  keep  down  the  weeds  the  ground  is  harrowed  two  or  three 
times  before  the  young  plants  get  far  above  the  surface.  After  this 
the  crop  is  given  from  one  to  three  cultivations,  is  hand  hoed  once 

or  twice  and  is  then  ridged. 
The  harvesting  is  done  by 
hand  with  the  aid  of  potato 
hooks,  the  marketable  tubers 
being  picked  into  baskets  as 
dug  and  then  sacked  in  the 
field,  the  cull  potatoes  being 
left  on  the  ground.  The  po- 
tatoes required  for  seed  pur- 
poses the  following  year  are 
usually  harvested  in  Decem- 
ber and  stored  in  sacks  or 
in  bulk  in  large  piles  on  the 
levees.  Often  the  only  pro- 
tection given  this  seed  stock  is 
a  covering  of  tule  stalks  or  a 
more  or  less  open  shed.     (See 

V\<i;.  1. — Seed  potatoes  stored  on  the  levee        „  . 

and  sprouting  badly.  hg.   J  • ) 


v£P?&£  -  JfaJL  LiJ 


THE  WEAK  POINTS  IN  THIS  SYSTEM  AND  THEIR  RELATION  TO  LOW 

YIELDS 

Owing  to  the  fact  that  experiments  are  now  being  conducted  to 
determine  the  best  cultural  methods  for  use  in  the  delta  section,  a 
discussion  of  this  feature  of  potato  growing  will  be  postponed  until 
some  definite  results  have  been  obtained.  The  principal  object  of  this 
paper  is  to  call  to  the  attention  of  the  farmers  and  owners  of  lands 
in  this  and  other  sections  of  the  state  where  similar  conditions  exist 
the  great  importance  of  making  certain  changes  in  their  methods  of 
handling  the  potato  crop.  Experience  has  already  shown  it  to  be 
imperative  that  such  changes  should  be  made  if  the  industry  is  to 
continue  to  thrive. 

Storage  of  Seed. — Owing  to  the  large  acreage  devoted  to  potatoes 
by  the  individual  growers  and  to  the  slow  method  of  planting,  with 
the  consequent  lengthy  period  needed  for  this  work,  the  seed  stock 
under  present  conditions  of  storage  becomes  badly  sprouted  long  be- 
fore planting  is  finished.  The  sprouts  often  grow  from  12  to  18  inches 
and  the  tubers  become  much  softened.  This  sprouting  uses  up  large 
quantities  of  the  food  material  stored  in  the  potatoes  which  should 
go  to  feed  the  young  plants  in  the  field;  moreover,  when  the  sprouts 
are  broken  off  and  the  tubers  cut  up  and  planted  many  of  the  small 
pieces  fail  to  sprout  again  and  there  is  a  consequent  poor  stand  over 
the  field.  The  pieces  which  do  sprout  produce  weak  plants,  which  are 
easily  affected  by  disease  or  other  unfavorable  conditions  of  growth, 
such  as  cold  weather  or  too  much  or  too  little  moisture,  and  the  yield 
is  consequently  reduced. 

A  great  improvement  in  the  condition  of  seed  stock  could  be 
brought  about  by  the  construction  of  a  simple  type  of  frame  storage 
building  with  double  walls  filled  with  some  cheap  material  such  as 
barley  straw.  The  night  temperatures  throughout  the  spring  often 
run  as  low  as  40  degrees,  and  by  the  use  of  ventilators  at  the  top  and 
bottom  of  the  building,  which  could  be  opened  at  night  to  admit  the 
cold  air  and  closed  in  the  morning  to  shut  out  the  warm  air,  suffi- 
ciently low  temperatures  might  be  maintained  to  greatly  retard  the 
sprouting  of  the  potatoes.  The  best  temperature  for  the  storage  of 
potatoes  is  from  36  to  40  degrees  F.,  but  they  will  not  sprout  for  a 
considerable  length  of  time  under  slightly  warmer  conditions. 

Influence  of  Cull  Potatoes  and  Short  Rotation. — Another  practice 
which  is  indirectly  responsible  for  the  decreasing  yields  of  potatoes 
on  the  delta  lands  is  that  of  leaving  the  cull  potatoes  scattered  over 
the  fields  at  the  time  of  harvesting.    One  could  scarcely  devise  a  better 


method  for  spreading  the  diseases  which  are  now  playing  great  havoc 
with  the  potato  industry.  It  can  hardly  be  considered  a  rotation  to 
grow  potatoes  for  three  successive  years  after  the  reclamation  of  these 
lands,  and  then  every  other  year  thereafter.  Owing  to  the  mild 
winters  in  the  delta,  the  cull  potatoes  produce  a  large  volunteer  crop, 
and  the  preparation  of  the  soil  for  the  barley  crop  does  not  kill  out 
the  potato  plants ;  hence  they  form  an  almost  continuous  growth  upon 
the  land  from  year  to  year.  In  this  way  all  of  the  diseases  which 
affect  potatoes,  once  introduced  on  the  seed  tubers,  are  afforded  ample 
opportunity  of  living  over  in  the  soil  and  of  increasing  with  great 
rapidity.  The  custom  in  vogue  on  the  islands  of  having  annual 
tenants  who  move  from  camp  to  camp  every  year,  carrying  their  seed 
potatoes  with  them,  provides  the  means  for  the  general  distribution 
of  all  the  potato  diseases. 


,  >  *  *  ;&.-! 


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4» 


DISEASES  DIRECTLY  RESPONSIBLE  FOR  DECREASED  YIELDS 
lihizoctonia. — There  are  several  potato  diseases  which  have  become 
very  widespread  throughout  the  delta.     The  one  which  at  present  is 

probably  responsible  for  the  greatest  in- 
jury to  the  crops  is  Rhizoctonia.     This 

iisSSibMJGBP*-  *s   a   funn°us   disease   which   lives   over 

^  *  •  from   year   to   year   on   stored   potatoes 

and  also  in  the  soil  on  roots  of  various 
plants.  The  accompanying  photograph 
(fig.  2)  shows  its  appearance  upon  the 
potato. 

It  looks  very  innocent  upon  the  tu- 
bers and  does  not  usually  injure  them 
for  domestic  purposes.  It  is  likely  to 
pass  unnoticed  by  the  average  grower 
since  it  cannot  easily  be  detected  when 
the  potatoes  are  more  or  less  covered 
with  soil.  The  difficulty  with  which  it 
can  be  removed  by  rubbing  or  washing 
presents  about  the  only  test  by  which  it 
can  be  distinguished  from  the  soil  on  the 
tuber.  When  conditions  are  favorable 
for*the  sprouting  of  the  tubers  the  fungus 
spreads  among  them  rapidly,  and  after  the  potatoes  are  planted  it 
attacks  the  young  shoots  as  they  develop,  often  girdling  and  cutting 
off  the  smaller  ones  and  more  or  less  seriously  injuring  the  larger 
ones.     When  the  underground  stolons,  which  are  formed  to  produce 


\r 


*Sfc 


-V 


Fig.  2. — lihizoctonia  on  po- 
tato tuber.  (After  Orton,  Bu- 
reau of  Plant  Industry,  U.  S. 
Department  of  Agriculture.) 


m 


■a  t 


the  young  potatoes  develop,  the  fungus  also  attacks  them  and  prevents 
the  formation  of  tubers.  If  an  examination  is  made  of  the  growing 
plants  in  almost  any 
field  many  of  them  are 
likely  to  be  found  in  the 
condition  of  the  plant 
shown  in  the  accompa- 
nying  photograph    (fig. 

3). 

A  very  conservative 
estimate  of  the  amount 
of  damage  done  by  this 
disease  during  the  season 
of  1913  would  place  the 
average  loss  throughout 
the  delta  region  at  25 
per  cent,  or  an  actual 
financial  decrease  of  a 
million  dollars  in  the 
value  of  the  crop. 

This  disease  lives  on 
many  other  cultivated 
plants,  especially  le- 
gumes, and  the  only 
practical  method  which 
can  at  present  be  recom- 
mended for  getting  it  g- 
out  of  the  soil  is  a  long  rotation  of  crops  upon  which  it  does  not 
thrive.  After  it  is  once  starved  out  of  the  soil,  disease-free  seed  should 
be  planted. 

Wilt  Diseases. — Two  species  of  fungi  (Fusariiim  oxysporum 
Schlect.  and  Verticilium  alboatrum  Reink.  and  Berth.)  are  very  com- 
mon upon  the  potatoes  grown  in  the  delta.  Both  of  these  diseases 
produce  a  discoloration  of  the  stems  and  tubers  a  short  distance  be- 
neath the  surface  of  the  ground.  This  discoloration  in  the  tubers 
forms  a  more  or  less  incomplete  ring  in  the  vascular  portion  of  the 
potato  as  shown  in  the  accompanying  photograph  (fig.  4).  It  is  most 
prominent  at  the  stem  end  and  disappears  more  or  less  gradually, 
depending  upon  the  severity  of  the  attack,  toward  the  opposite  end  of 
the  tuber.  This  disease  causes  a  wilting  of  the  growing  plants,  due 
to  the  fact  that  the  growth  of  the  fungus  in  the  stems  cuts  off  the 
supply  of  water  from  the  roots.     It  becomes  much  more  noticeable 


-Potato  stems  affected  with  Rhizoctonia. 


6 

toward  the  end  of  the  growing'  season  and  on  the  drier  portions  of  the 
fields.  A  serious  feature  of  this  disease  is  that  it  forms  a  means  of 
entrance  for  other  fungous  and  bacterial  diseases  of  the  tubers  such 
as  "jelly  end"  and  dry  rot,  which  are  also  very  destructive  in  many 
places. 

The  wilt  diseases  are  introduced  into  the  soil  through  diseased  seed 
tubers,  and  no  potatoes  showing  a  discoloration  near  the  stem  end 

such  as  is  shown  in  the  cut  (see  fig.  4) 
should  be  used  for  seed  purposes. 
A  long  rotation  and  the  use  of  disease- 
free  seed  are  the  only  recommenda- 
tions that  can  be  made  for  the  control 
of  these  diseases. 

Scab. — This  is  a  disease  that  is  well 
known  to  all  the  potato  growers  of  the 
delta,  and  in  some  localities  and  under 
HI  l&mRSflBHBHHHHHH     certain  conditions  it  causes  consider- 

Fig.  4.-Potato  tubers  affected  able  loSS  throughout  the  section.  It 
with  wilt.  (After  Orton,  Bureau  is  introduced  through  the  use  of  dis- 
^ent^Vg"^.)"  S'  Depart"      ^sed  seed  tubers  and  becomes  much 

worse  on  alkali  soil  than  elsewhere. 
Tubers  affected  by  scab  should  either  be  treated  by  soaking  for  two 
hours  in  a  solution  of  formaldehyde  (one  pint  to  30  gallons  of  water), 
or  else  not  used  for  seed  purposes.  The  infection  is  likely  to  be 
present  in  such  a  small  amount  as  to  be  unnoticeable  and  great  care 
should  be  exercised  to  plant  clean  seed.  The  treatment  of  seed  pota- 
toes with  formaldehyde  is  not  advisable  if  the  tubers  have  sprouted 
badly,  as  a  poor  stand  is  likely  to  result  from  its  use.  Moreover,  this 
treatment  is  not  alone  sufficient  to  prevent  infection  of  the  crop  if 
the  soil  has  already  been  infected.  It  is  necessary  to  practice  a  long 
rotation  to  remove  the  disease  from  the  soil  after  it  has  once  gained 
a  foothold. 

Tuber  Moth. — For  some  reason,  probably  because  of  the  large 
amount  of  water  used  for  irrigation  in  this  locality,  the  tuber  moth 
(Phthorimaea  operculella  Zell.)  has  not  thus  far  caused  very  serious 
damage  to  potatoes  in  the  soil  before  harvesting.  This  is  true,  at 
least,  for  the  peat  soils  which  are  kept  well  watered,  although  on 
higher  land  the  moth  has  sometimes  proved  quite  injurious.  Condi- 
tions may  arise,  however,  under  which  this  pest  may  become  more 
generally  serious,  and  it  is  advisable  to  prevent  its  multiplication  as 
far  as  is  possible.  Potatoes  examined  by  the  writer  as  they  were 
being  dug  from  a  typical  moist,  peat  soil  showed  but  one  or  two  per 


cent  of  tuber  moth  infestation.  Several  days  later,  however,  an  exami- 
nation of  the  cull  tubers  which  had  been  left  upon  the  ground  in  the 
same  field  showed  that  90  per  cent  of  them  were  infested  with  this 
pest.  This  indicates  how  rapidly  the  moths  are  multiplied  through 
the  practice  of  leaving  cull  potatoes  upon  the  ground.  The  moth  also 
attacks  potatoes  in  sacks,  and  great  care 
should  be  taken  to  keep  all  marketable 
stock  well  covered  so  that  the  moth  can-  ...,,.,. 

not  gain  access.     (See  fig.  5.) 

The  Nematode  Gallworm  or  Eel- 
worm,. — This  disease  of  potatoes  and  of 
many  other  crops  is  caused  by  a  minute 
nematode  worm  (Heterodera  radicicola 
(Greef.)  Mull.).  While  it  has  not  thus 
far  become  widely  prevalent  in  the  delta 
as  a  serious  pest  on  potatoes,  it  is  known 
to  be  present  in  certain  fields  in  this 
locality  and  has  caused  much  trouble  in 
other  parts  of  the  country  and  in  the 
old  world.  The  accompanying  photo- 
graphs (figs.  6  and  7)  shows  the  appear- 
ance of  tubers  infested  with  this  para- 
site. It  may  be  present  in  many  tubers 
in  such  small  quantities  as  to  render  it 
difficult  of  detection  and  may  become 
widespread  through  the  planting  of  in- 
fested potatoes.  All  potato  growers 
should  be  very  careful  that  their  seed  is  absolutely  free  from  this  pest. 
It  is  also  of  especial  importance  to  the  landowners  to  keep  their  soil 
free  from  such  infestation,  since  its  eradication  when  once  it  is  intro- 
duced is  a  very  difficult  task. 

All  seed  potatoes  should  be  carefully  inspected  by  some  one  who 
is  familiar  with  this  trouble  and  no  seed  stock  should  be  planted  about 
which  there  is  any  suspicion  as  to  the  presence  of  the  parasite.  Before 
buying  potatoes  for  seed  purposes  planters  should  make  sure  that  the 
locality  in  which  they  were  grown  is  not  infested. 

The  nematode  worm  thrives  on  a  large  number  of  cultivated  plants, 
which  fact  makes  it  all  the  more  important  that  every  precaution 
should  be  used  to  keep  the  land  free.  It  should  not  be  taken  for 
granted  that  conditions  in  the  delta  are  unfavorable  for  the  spread 
of  this  trouble  and  every  effort  should  be  made  to  restrict  its  distri- 
bution.    After  once  being  introduced  into  the  soil  it  is  very  easily 


Fig.  5.— Potato  showing  com- 
paratively light  injury  from 
the  potato  tuber  moth  (PhthorU 
maea  operculella) .  (After  Chit- 
tenden, Bureau  of  Entomology,. 
U.  S.  Department  of  Agricul- 
ture.) 


8 

carried  into  other  fields,  either  on  the  roots  of  plants  or  in  the  soil  on 
boots  and  farm  implements,  or  in  irrigation  water.  It  is  all  the  more 
dangerous  because  of  the  fact  that  it  attacks  a  great  variety  of  farm 


I  iy 


Fig.  6 

Potato  infested  with  eelworms. 
Department  of  Agriculture.) 


Fig.  7 
(After  Orton,  Bureau  of  Plant  Industry,  U.  S. 


crops  and  weeds,  including  crops  now  grown  in  the  delta  such  as 
onions,  beans,  celery,  and  alfalfa.  It  is  very  difficult  to  eradicate 
completely  the  nematode  after  it  has  once  become  well  established  in 
the  soil,  but  it  is  possible  to  reduce  the  amount  of  infestation  by 
growing  crops  upon  which  it  does  not  thrive.  Some  of  the  crops 
which  are  little  or  not  at  all  affected  by  this  parasite  are  barley, 
sorghum,  milo,  timothy,  redtop,  and  oats. 


GENERAL  RECOMMENDATIONS 

Since  all  of  the  diseases  which  affect  the  potatoes  of  the  delta 

have,  without  much  doubt,  been  introduced  by  planting  infected  seed, 

it   is  evident  that  they  cannot  be  eradicated  so  long  as  diseased  seed 

stock  is  used.     To  eradicate  any  or  all   of  these  diseases  from  soil 


already  infected  it  is  necessary  that  the  cull  potatoes  be  removed  from 
the  field  at  the  time  the  marketable  tubers  are  harvested.  This  will 
not  be  a  great  hardship  to  the  grower,  as  the  expense  of  gathering  the 
cull  potatoes  into  separate  baskets  at  the  time  the  others  are  picked  up 
will  not  be  great.  Moreover,  the  cull  potatoes  are  valuable  for  stock 
feeding  purposes,  and  this  economy  more  than  offsets  the  expense  of 
picking  them  up.  They  make  an  excellent  food  for  hogs,  especially 
when  cooked  and  fed  with  corn  or  other  grain.  Horses  also  eat  con- 
siderable quantities  of  them  with  relish.  Besides,  even  if  these  cull 
potatoes  cannot  be  used  for  feeding  stock,  it'  will  be  an  expenditure 
well  worth  while  for  the  landowners  to  have  them  taken  off  the  fields 
in  order  to  reduce  the  size  of  the  volunteer  crop  and  prevent  the 
spread  and  multiplication  of  the  diseases  mentioned  above. 

Since  it  usually  takes  two  years  to  get  rid  of  the  volunteer  potatoes 
even  when  other  crops  are  grown  following  the  potato  crop,  a  rotation 
shorter  by  one  or  two  years  will  produce  as  good  results  as  a  corre- 
spondingly longer  rotation  under  the  present  system.  After  the  in- 
fected fields  are  freed  from  volunteer  potatoes  and  before  good  crops 
of  marketable  potatoes  can  be  produced  it  will  be  necessary  to  carry 
a  rotation  of  other  crops  for  several  years  in  order  to  starve  the  diseases 
out  of  the  soil. 

The  experience  which  owners  and  tenants  have  had  with  potatoes 
on  the  older  reclaimed  areas  should  impress  the  owners  of  the  new 
areas  and  their  tenants  with  the  desirability  of  keeping  the  new  land 
as  far  as  possible  free  from  potato  disease.  This  can  only  be  accom- 
plished by  rigidly  inspecting  the  seed  potatoes  and  discarding  all 
diseased  stock.  It  is  a  difficult  matter  at  the  present  time  to  obtain 
seed  potatoes  which  are  not  affected  with  one  or  more  of  the  diseases 
mentioned.  Every  effort  should  be  made,  however,  to  secure  the  best 
possible  seed,  even  though  this  is  more  expensive  than  the  ordinary 
stock. 

Many  of  these  diseases  are  so  widespread  over  the  country  that 
it  would  be  advisable  for  the  growers  to  co-operate  in  securing  some 
locality  where  the  soil  has  not  yet  become  inoculated  and  where  disease- 
free  seed  potatoes  may  be  grown.  If  the  tenants  are  not  willing  to 
do  this,  it  would  be  to  the  interest  of  the  landowners  to  secure  disease- 
free  seed  stock  and  stipulate  that  the  tenants  plant  only  such  seed  as 
the  owners  furnish. 

The  seed  potatoes  for  the  delta  come  originally  from  Oregon  or 
other  nearby  states,  the  growers  planting  a  small  amount  of  this  seed 
every  year  to  furnish  seed  stock  for  the  general  crop  the  following 
year.     The  prevailing  opinion  is  that  while  this  seed  does  not  yield 


10 

as  well  during  the  first  year  as  does  the  home-grown  seed,  yet  the 
latter  stock  must  be  renewed  every  other  year.  In  other  words,  the 
growers  believe  that  potatoes  grown  in  the  delta  two  or  more  seasons 
lose  their  vitality  to  such  an  extent  as  to  make  it  advisable  to  get  a 
new  stock  from  another  locality.  Whether  this  view  of  the  situation 
is  correct  needs  to  be  demonstrated  by  careful  experimentation. 

In  whatever  locality  the  seed  potatoes  are  grown,  they  should  be 
selected  for  productiveness  and  freedom  from  disease.  Trained  men 
are  required  to  handle  this  work  successfully,  and  growers  should  not 
be  averse  to  paying  a  higher  price  for  good  seed  stock  than  for  the 
miscellaneous  product  now  upon  the  markets.  With  potatoes,  as  with 
other  crops,  it  is  of  prime  importance  that  good  seed  stock  be  used, 
since  only  in  this  way  can  permanent  success  be  obtained. 


CROPS  SUITABLE  FOR  ROTATION  WITH  POTATOES 

Alfalfa  has  usually  been  considered  a  good  crop  to  use  in  any 
rotation  where  potatoes  are  grown.  Its  use,  however,  has  become 
questionable  owing  to  the  fact  that  Rhizoctonia  may  be  carried  over  to 
the  potato  crop  on  the  roots  of  alfalfa.  This  is  equally  true  of  other 
leguminous  crops  such  as  peas,  beans,  and  clovers.  The  legumes  are 
also  infested  with  eelworm  when  the  soil  in  which  they  are  planted 
contains  this  parasite. 

The  crops  which  are  least  likely  to  carry  any  of  the  potato  diseases 
are  barley,  oats,  corn,  buckwheat,  broomcorn,  rye  grass,  hemp,  and 
celery.  Onions  are  affected  with  Fiisarium,  and  it  has  been  noticed 
that  "jelly  end"  is  worse  on  potatoes  following  onions  than  elsewhere. 


SUMMARY 

The  use  of  badly  sprouted  seed  potatoes  causes  a  considerable 
decrease  in  stand  and  yield. 

Potato  diseases  are  causing  the  growers  immense  losses  every  year. 

Cull  potatoes  are  responsible  in  large  measure  for  the  rapid  increase 
of  all  potato  diseases,  and  should  therefore  be  removed  from  the  fields 
at  harvest  time. 

The  short  rotation  system  practiced  in  the  delta  is  an  important 
factor  in  the  rapid  distribution  of  potato  diseases. 

Long  rotations  of  certain  crops  and  the  use  of  disease-free  seed 
potatoes  are  the  means  which  should  be  adopted  to  overcome  the 
diseases  and  increase  the  vields. 


11 

The  following  publications  will  be  found  of  value  to  those  desiring 
further  information  concerning  potato  growing : 

Farmers'  Bulletin,  No.  544,  Potato  Tuber  Diseases. 

Bureau  of  Plant  Industry,  Circular  No.  23,  Potato  Diseases  in  San  Joaquin 
County,  California. 

Bureau  of  Plant  Industry,  Circular  No.  91,  The  Nematode  Gall  worm  on 
Potatoes  and  Other  Crop  Plants  in  Nevada. 

Farmers'  Bulletin,  No.  533,  Good  Seed  Potatoes  and  How  to  Produce  Them. 

All  of  these  publications  can  be  obtained  from  the  Secretary  of 
Agriculture,  Washington,  D.  C. 


